1. Field
Embodiments relate generally to a method of manufacturing a printed circuit board having embedded resistors. More particularly, the embodiments relate to a method of manufacturing a printed circuit board having embedded resistors, in which contact pads are formed by filling via holes formed on electrode pads with oxidation-resistant conductive material, and resistors are formed on the contact pads, thus not only reducing the differences between the resistance values of the embedded resistors, but also preventing erosion from occurring between the electrode pads and the resistors.
2. Description of the Related Art
In electronic products including recent portable electronic devices, various demands from consumers are increasing. In particular, consumers' desires for multiple functions, a small size and light weight, a high speed, a low price, increased convenience of movement, real-time wireless connection with the Internet, refined design and the like cause developers, designers and manufacturers to feel greatly burdened in the manufacturing of high-quality products. Such increased competition leads rival manufacturers to market new models on a daily basis. This increases again the burden on all persons concerned.
As the functions of products becomes diverse in this manner, the number of passive elements increases relative to the increase in the number of Integrated Circuits (ICs), and thus the size of portable terminals also increases. Generally, in an electronic device, a plurality of active elements and a plurality of passive elements are mounted on the surfaces of a circuit board. In order to facilitate the transmission of signals between the active elements, a large number of passive elements are surface-mounted in the form of discrete chip resistors.
As a part of an effort to realize high density mounting for an electronic system, development for embedded Printed Circuit Boards (PCBs) is being conducted by the large number of manufacturers concerned. Passive elements embedded in such a board are classified into Resistors R, inductors L and capacitors C according to type, and embedded elements are classified into existing thin passive elements, film elements formed using printing or sputtering, and plating-type elements based on plating according to size and form. However, discrete chip resistors, that is, passive elements have a limitation in the ability to satisfy the trend of making electronic products light, thin, short and small using only, have a problem with the use of space, and have a disadvantage in that the cost is increased.
Accordingly, various attempts to embed film-type resistors having a thickness of 15˜25 μm, which belong to passive elements, in a board have been made. In order to embed such film-type resistors in a board, methods such as screen printing, sputtering and plating are employed. In particular, screen printing is advantageous in that the number of element mounting processes can be reduced and the cost can be reduced. Furthermore, screen printing is advantageous in that the reliability of contact can be improved, light weight can be realized, and environmental loads can be reduced, because the number of solder joints is reduced.
Technology for embedding resistors in a PCB using an existing printing technique includes various forms and processes. According to an embodiment of a prior art, as shown in FIGS. 2A and 2B, resistors 5 are formed by forming electrode pads 1 and 2 on an insulating board 6, and printing resistor paste between the electrode pads 1 and 2, which are spaced apart from each other, using a photoresist film 3 as a resist. However, the prior art is problematic in that poor printability of the resistors 5 results due to the differences in height between the electrode pads 1 and 2 and the insulating board 6, so that the formed shapes thereof become irregular, thereby resulting in increased differences between the resistance values. When the resistance values are measured after the resistor paste has been formed through printing as described above, a problem occurs when performing laser trimming if the resistance values are greater or much smaller than a target resistance value. The trimming cannot be performed when the resistance values of the printed resistors are large, and a problem with the reliability thereof may be caused when the resistance values of the printed resistors are very small. Such error results in decreased yield with increased incidence of defects and ultimately degrades the performance of products, and therefore it is considered to be the factor most urgently requiring improvement.